1. Field of the Invention
The present invention relates to a substrate processing apparatus and a substrate plating apparatus, and more particularly to a substrate processing apparatus and a substrate plating apparatus for filling a metal such as copper (Cu) or the like in fine interconnection patterns (trenches) on a semiconductor substrate, and a substrate processing apparatus for electrolyzing a surface of a substrate in a plurality of stages.
2. Description of the Related Art
Aluminum or aluminum alloy has generally been used as a material for forming interconnection circuits on semiconductor substrates. As the integrated density has increased in recent years, there is a demand for the usage of a material having a higher conductivity as an interconnection material. It has been proposed to plate a substrate having interconnection pattern trenches thereon to fill the trenches with copper or its alloy.
Various processes are known, including CVD (chemical vapor deposition), sputtering, etc. for filling interconnection pattern trenches with copper or its alloy. However, the CVD process is costly for forming copper interconnections, and the sputtering process fails to embed copper or its alloy in interconnection pattern trenches when the interconnection pattern trenches have a high aspect ratio, i.e., a high ratio of depth to width. The plating process is most effective to deposit a metal layer of copper or its alloy on a substrate to form copper interconnections thereon.
Various processes are available for plating semiconductor substrates with copper. They include a process of immersing a substrate in a plating liquid held at all times in a plating tank, referred to as a cup-type or dipping-type process, a process of holding a plating liquid in a plating tank only when a substrate to be plated is supplied to the plating tank, an electrolytic plating process of plating a substrate with a potential difference, and an electroless plating process for plating a substrate with no potential difference.
Conventional plating apparatuses for plating substrates with copper have a loading/unloading unit for placing a substrate cassette to load and unload substrates, various units for plating, for performing its supplementary process, and for cleaning and drying a plated substrate, and a transfer robot for delivering substrates between the loading/unloading unit and the various units. The loading/unloading unit, the various units, and the transfer robot are disposed in a horizontal plane. A substrate is taken out of a substrate cassette placed in the loading/unloading unit, delivered between the units, processed by the units, and thereafter returned to the substrate cassette in the loading/unloading unit.
With the conventional plating apparatus, however, various structural limitations imposed by paths to transfer substrates and paths of the transfer robot make it difficult to achieve an efficient layout of the loading/unloading unit, the transfer robot, and the various units within one facility. Another problem is that the conventional plating apparatuses suffer some maintenance problems. These drawbacks are also found in other substrate processing apparatuses, such as a polishing apparatus for chemically and mechanically polishing (CMP) substrate surfaces and the like.
Furthermore, the conventional plating apparatuses have separate units for plating, pretreating, and otherwise treating substrates, and substrates are delivered to and processed by these separate units. Therefore, the plating apparatus is considerably complex in structure and difficult to control, takes up a large installation area, and is manufactured at a high cost.
When LSI circuit interconnections are formed by an electrolytic plating process, they have a microscopic structure having interconnection widths and contact hole diameters in a range smaller than 0.15 μm and an aspect ratio (ratio of depth to width) of 6 or more. For embedding interconnection trenches according to copper sulfate plating alone to form such a microscopic structure, it is necessary to finely control additives and energizing conditions in the plating process. Due to variations in formed seed layers, voids tend to be formed in bottoms and side walls of interconnections and seams are liable to be formed in central regions of interconnections, making those interconnections defective.
For embedding fine interconnections fully in corresponding trenches, it is necessary to meet both requirements for improved bottom coverage and side coverage by increasing the uniform electrodeposition capability of a plating process, and for an increased bottom-up filling capability to preferential embedding from interconnection bottoms.
One proposal for achieving both a uniform electrodeposition capability and a bottom-up filling capability is an electrolytic plating process that is carried out in two stages. According to such an electrolytic plating process, for example, a substrate is plated in a first stage according to a process of a high uniform electrodeposition capability using a complex bath for increased coverage, and then interconnection trenches in the substrate are embedded using a copper sulfate bath to which an additive to increase the bottom-up filling capability is added. The plating apparatus that is used in this process comprises two cup-type or dipping-type plating cells connected in series with each other.
As another process of embedding fine interconnections fully in corresponding trenches, there has been proposed a plating process that is performed in two stages, i.e., an electroless plating stage and an electrolytic plating stage. According to such a proposed plating process, an auxiliary reinforcing seed layer is formed on a seed layer that has been formed by sputtering, for example, according to an electroless plating process, thus well preparing the overall seed layer including the auxiliary seed layer for a subsequent process. Then the seed layer is plated according to an electrolytic plating process to embed fine interconnections reliably in corresponding trenches.
The two-stage electrolytic plating process or the plating process performed in an electroless plating stage and an electrolytic plating stage, as described above, needs to have a plurality of plating apparatuses, each having a loading/unloading unit, a plating unit, processing units, and a transfer robot, which are arranged in juxtaposed relation to each other. Since these plating apparatuses occupy a large installation space in a clean room, the clean room needs to be large in size. Those plating apparatuses are responsible for an increase in the cost of the overall system. In addition, it is complex and time-consuming to deliver substrates between the plating apparatus.
Furthermore, when an electrolytic plating process is carried out on a substrate while a surface to be plated of the substrate is facing downwardly, and an electroless plating process is carried out on a substrate while a surface to be plated of the substrate is facing upwardly, a substrate reversing machine is required between the two plating apparatuses. The required substrate reversing machine poses an obstacle to attempts to make the overall system more compact and less costly.
After a substrate has been processed by one of the plating apparatuses, the substrate is dried and placed in a wafer cassette, and then delivered to the other plating apparatus. During these subsequent steps, the plated surface of the substrate may possibly be contaminated, tending to cause a plating failure such as an embedding failure or an abnormal precipitation of plated metal in the next plating process. In the drying step, the plated surface of the substrate may possibly be oxidized.